1. Field of the Invention
The present invention relates to polymers useful as a base resin for a resist material useful for microfabrication for ultra LSI, resist materials containing the polymers and patterning method using the resist materials.
2. Description of the Related Art
With a recent thrust towards high integration and high operation speed in LSI devices, there has recently been a demand for miniaturization of a pattern rule. Under such a situation, far UV lithography is regarded as promising next-generation microfabrication technology. In particular, photolithography using a KrF or ArF excimer laser light as a light source is eagerly desired to reach the practical level as a technique indispensable for nano-microfabrication capable of achieving a feature size of 0.3 μm or less.
As a resist material for KrF excimer laser, polyhydroxystyrene having both transparency and etching resistance, each on a practical level, has become a standard base resin. As a resist material for ArF excimer laser, on the other hand, polyacrylic or polymethacrylic acid derivatives having an adamantyl structure on the side chain thereof have been used relatively frequently as described, for example, in Japanese Patent Provisional Publication No. 9-73173/1997 or 9-90637/1997, but they do not always exhibit their performances fully.
Resist materials containing a polyacrylic or polymethacrylic acid derivative as a base resin show good sensitivity and resolution on pattering by exposure to light and development, but their dry etching resistance is markedly low. Introduction of many polycyclic structures typified by an adamantane structure is effective for heightening a carbon density, thereby improving dry etching resistance. When a polymer having many acid decomposable units having an adamantane structure, more specifically, many (meth)acrylic acid units protected by a 2-methyl-2-adamantyl group is used as a base resin, however, its dull acid decomposition reactivity leads to insufficient resolution. Resist materials using such a polymer as a base resin involve problems such poor capacity of forming thin lines upon etching, high temperature dependence upon heat treatment for an acid decomposition reaction, and remaining of unreacted products on the substrate as a foreign matter after patterning. Incidentally, the term “(meth)acrylate” as used herein means methacrylate or acrylate.